The invention relates to a filter bag for pocket air filters (air filters having pockets), comprising two side walls whereby both lateral edges of said side walls and the edge of the base are welded to each other. Said side walls are made of an air-permeable filter material, which may be ultrasonically welded, and whereby at least part of the surface of said side walls is joined by means of interconnected welded spacer elements running substantially parallel to said side walls.
Filter bags of this type are usually arranged next to each other with a space in between to form a pocket air filter. The best possible even (air) flow in all areas of the filter layer is the goal to keep the rate of flow at a minimum and to obtain optimum utilization of the filter layer. Thus it is necessary in pocket air filters to keep the side walls of each single filter bag at an optimum distance from one another since only in this way optimum spacing between the neighboring filter bags can be maintained.
In case of filter bags that are preferably made from non-weldable filter material, this spacing is achieved by spacer seams, which have to be subsequently sealed with hot-melt adhesive. This sewing process, which can also be used for weldable filter materials, has however the disadvantage that the necessary sealing of the needle holes is performed partly incomplete. Besides, the perforation of the filter material.
To achieve dependable sealing of the filter bag and to prevent tearing, there is known from the type of filter bag mentioned in the beginning to weld the two filter side surfaces to the spacer elements, which are made of tubes consisting of flexible material and which then form the two side walls. The therefor necessary effort in labor is relatively high and costly in comparison to the sewing process, especially since the spacer elements made of tubes have double walls.
It is therefore the object of the invention to provide a filter bag of the type mentioned in the beginning that is of simple design and can be manufactured with low expenditure of labor and material. Thereby an optimum configuration of the filter bag in its operational state is to be guaranteed to maintain its optimum spacing between the two side walls.
This object is achieved according to the invention in that the spacer elements are formed by an intermediate layer made from a strip of flexible material that is alternately welded to one of the side walls.
With this alternate welding to one of the side walls, it is achieved that the intermediate layer takes on a fan-shaped (zigzag-shaped) design. Thereby the side walls are dependably maintained at the preset optimum spacing from one another whereby the respective diagonal direction of the spacer elements formed by said fan-shaped intermediate layer result in a very effective stabilization of the two side walls against relative displacement. Thus it is made possible to considerably increase the number of individual juxtaposed filter bags within the preset grid width of pocket air filters (currently a maximum of 12 filter bags at a with of 592 mm). This gives the advantage of increased dust collection capability and longer durability.
The production of the filter bag is considerably simplified since instead of single tube-shaped spacer elements, which have to be individually installed and welded, there is now only one interconnected intermediate layer installed, which is alternately joined to one or the other side wall by ultrasonic welding. The filter bag can therefore be manufactured very easily and cost-effectively; it is of simple design and has an optimum configuration of filter surfaces, which are maintained at an optimum spacing to one another so that a free (air) flow is guaranteed for a plurality of parallel aligned filter bags, which are arranged next to one another as close as possible.
The intermediate layer is preferably joined alternately with the one or the other side wall by welding seams created through ultrasonic welding whereby said welding seams run substantially parallel to the lateral edges.
According to one of the preferred embodiments of the invention it is proposed that the intermediate layer consists of a single strip of material and is welded to the two lateral edges of both side walls. Thereby the intermediate layer runs continuously from one lateral edge to the other lateral edge of the filter bag. This contributes to the stabilization of the filter bag and simplifies production.
The neighboring welding seams of the intermediate layer are preferably arranged at equal distance to one another. Thereby the same design is provided substantially across the entire width of the filter bag.
According to a preferred embodiment of the filter bag it is proposed that the intermediate layer is disposed at a distance from the base, and that the two side walls in the area between the base and the intermediate layer are joined directly with one another by welding seams that are running substantially parallel to the lateral edges. Thereby the filter bag is tapered from its in-flow opening toward the base so that a general even (air) flow is ensured through the entire length of the filter bag.
The invention relates additionally to an advantageous method for the production of filter bags of this type. Starting from a known method whereby two layers of filter material are welded together by ultrasound at both lateral edges and at the base whereby spacing elements, which are arranged in between, are also welded thereto by ultrasound; the method according to the invention is characterized in that two continuous inserted strips of filter material are welded at alternately superposed welding seams, which run transversely to the longitudinal direction of the strip, to a continuous intermediate layer strip inserted in between, whereby ultrasonic welding occurs through both strips of filter material and through the intermediate layer strip, and whereby during consecutively performed welding processes a non-weldable separating plate is inserted alternately between the intermediate layer strip and the one or the other strip of material, respectively.
A continuous manufacturing process has been made possible hereby for the first time, which may be carried out very rapidly and simply and which is therefore cost-effective. Instead of the complicated and labor-intensive insertion of separating plates by hand, there are now separating plates, which are arranged between each of the intermediate layers and each of the strip of filter material, and which are pushed into the welding area according to demand whenever the welding of superposed layers is to be prevented at a particular place. In this way it is very simple, in view of production engineering, to weld the intermediate layer strip alternately to one or the other strip material while forming a side wall.
According to a preferred embodiment of the invention it is proposed that the two separating plates are designed as separating straps, which run cross-wise to the longitudinal strip direction and which are alternately moved in and out of the welding area in the direction of the moving strip. The separating straps move in very short strokes so that a relatively rapid operating process is guaranteed.
During welding of the lateral edges, the two separating plates or separating straps remain in a retracted position relative to the welding area so that the side walls may be welded to the intermediate layer at the lateral edges.
The two strips of filter material and the intermediate layer strip may be fed into a welding station by controlled forward-feed steps wherein there is at least one ultrasonic welding head, which extends across the longitudinal strip direction and which is disposed at the opposite side of a welding counter-surface. Thereby one single welding station is sufficient to perform all transverse welding on a filter bag, one after the other, in the operating area of the ultrasonic welding heads (sonotrodes).
Preferably there are a plurality of welding heads at the welding station which are arranged side by side and transverse to the strip direction, and which may be controlled individually. Thus it is possible to make welding seams of various lengths and especially perform direct welding of the two side walls in the area near the base of the filter bag.